Apparatus for the vacuum degassing of molten metal



W. SIECKMAN @et l?, 1967 APPARATUS FOR THE VACUUM DEGASSING OF MOLTEN MFTALl Filed April 28, 1965 INI/EN TOR. Me'f 5 United States Patent G APPARATUS FOR THE VACUUM DEGASSING OF MOLTEN METAL Walter Sieckman, Canonsburg, Pa., assigner to Mc Graw Edison Company, Milwaukee, Wis., a corporation of Delaware Filed Apr. 28, 1965, Ser. No. 451,449 4 Claims. (Cl. 266-34) ABSTRACT F THE DISCLOSURE A vacuum degassing vessel having a molten metal conducting pipe that is continuously refractory covered over the portion subject to immersion in molten metal and includes induction coils in the refractory material for delivery of heat to the melt.

This invention relates to apparatus for the vacuum degassing of molten metals and, more particularly, to means for maintaining molten metal at an elevated temperature during a vacuum degassing operation.

The metallurgy of certain metal alloys requires the reduction of such elements as oxygen, carbon and hydrogen. Because chemical reactions involving these elements have a gas phase and can be made to occur at reduced pressures, their removal can be accomplished expeditiously by treating the melt in a vacuum chamber.

The various handling procedures involved in vacuum treating a melt generally include tapping of the furnace, transfer of the molten metal from furnace to the vacuum treating apparatus, the vacuum treatment itself, transfer of the molten metal from the vacuum treating apparatus to the mold and, finally, casting. The vacuum `degassing operation adds considerable time to the period between tapping and teaming of a melt so that heat must be added to the melt to prevent a temperature drop below that required for successful casting.

The general type of vacuum degassing apparatus used to illustrate the preferred embodiment of the instant invention is one wherein a vacuum vessel is disposed above a ladle of molten metal and the two are arranged for relative movement toward and away from each other. One or more molten metal intake and discharge pipes extend downwardly from the lower end of the vessel for immersion below the surface of the molten metal wherein the molten metal may be drawn into the degassing chamber by movement of the chamber and ladle toward each other and discharged therefrom upon relative movement in the opposite direction. In another well known type of vacuum degassing apparatus, molten metal is carried into the vacuum chamber by a stream of inert gas injected into the molten metal conducting pipe.

One prior art method of heating a vacuum degassing chamber was by means of a graphite resistance heating rod. Such graphite resistance heating elements had to be suiliciently remote from the inlet and discharge pipes to prevent contact with the molten metal, which would damage the heating element and result in the addition of unwanted carbon to the melt. As a result, heat losses were relatively high and, in addition, a relatively expensive high domed chamber was required.

Another type of heating device for vacuum degassing chambers having a pair of molten metal conducting pipes, consists of a closed ferromagnetic core which links one pipe and a primary transformer winding wherein a secondary current would be induced within the molten metal in the vessel and in the two pipes. This type of apparatus was not entirely satisfactory, because the magnetic core and primary winding were directly exposed to the heat of the metal within the ladle. Another shortcoming of this type of device is the fact that it was limited to a degassing vessel having two pipes. In addition, the presence of the magnetic core and primary winding below the vessel restricted the degree of relative travel between the degassing vessel and ladle.

It is an object of the invention to provide a new and improved heating system for vacuum degassing vessels.

Another object of the invention is to provide a vacuum degassing vessel having a molten metal conducting pipe atlxed to its lower end wherein a refractory covers at least a portion of the pipe and an induction coil is disposed in the refractory. Another object of the invention is to provide such a vacuum degassing vessel wherein the refractory comprises a lining for the pipe. Still another object of the invention is to provide such a Vacuum degassing vessel wherein the refractory comprises a `jacket covering at least a portion of the outer surface of the pipe.

These and other objects and advantages of the instant invention will become more apparent from the detailed description thereof taken with the accompanying drawings in which:

FIG. 1 is a side elevational view, partly in section, of vacuum degassing apparatus incorporating the instant invention; and

FIG. 2 is a cross sectional view of the molten metal conducting pipe of the vacuum degassing chamber illustrated in FIG. 1.

In general terms, the invention comprises a vacuum degassing vessel having at least one refractory lined, molten metal conducting pipe extending from its lower end and which has an induction coil embedded in the refractory material covering at least a portion of the pipes surface.

Referring now to the drawings in greater detail, FIG. l shows vacuum degassing apparatus comprising a vacuum degassing vessel 10, a ladle 11 containing molten metal 12 and a lifting mechanism 14 for supporting the vessel 10 and for lifting its vertically relative to the ladle 11. The degassing vessel 10 includes a steel shell 15 which encloses and provides support for an inner refractory lining 16, which defines a vacuum chamber 17. A molten metal conducting pipe 18 is aixed to the lower end of the vessel 10 and has a cylindrical bore 19 which cornmunicates with the interior of the chamber 17.

The chamber 17 is connected to a suitable evacuating apparatus 13 by a conduit 20 which is aixed in a sealed relation to the shell 15 adjacent an aperture 21 in the roof of the refractory lining 16.

The lifting mechanism 14 includes a platform 22 upon which the vessel 1Q is mounted and a plurality of coordinated hydraulic rams 23 for moving the platform 22 and the vessel 10 vertically relative to the ladle 11. Control of the hydraulic rams 23 is effected by an operator stationed at a remote location. It will be appreciated by those skilled in the art that while the vessel 10 is shown to be vertically movable in the illustrate-d embodiment, the device operates equally as well if the vessel 10 is stationary and the ladle 11 movable.

After the ladle 11 of molten metal 12, such as steel, has been positioned below the vessel 10, the latter is lowered until the pipe 18 extends a predetermined distance below the surface of the melt 12. The evacuating apparatus 13 is then actuated to produce a partial vacuum within the chamber 17. As a result of the difference in pressure between the interior of the chamber 17 and the atmospheric pressure acting on the surface of the melt 12, a portion of said melt identified by the reference 12, is vforced upward through the bore 19 in the pipe 18 and into the chamber 17 where gases dissolved therein are drawn oif by the operation of the partial vacuum. After this portion 12' of the melt 12 has been degassed for a predetermined length of time, the vessel is raised,

thereby causing the melt 12' to discharge back into the ladle 11.

The lower end of the pipe 18, however, remains below the surface of the melt 12 to maintain a partial vacuum within the chamber 17. This process may then be repeated by successively lowering and raising the vessel 10 until the desired degree of total degasication has been achieved. Because the degassed portion of the metal 12 has a greater density than the untreated portion of the metal in the ladle 12, the degassed metal 12 settles to the bottom of the ladle 11 upon discharge from the vessel 10 so that succeeding portions of the melt 12 which are drawn into the chamber 17 from the upper portion of the ladle will be substantially untreated.

Reference is now made to FIG. 2, which in greater detail shows the molten metal conducting pipe 18 to include a steel shell 2S, an inner refractory lining 26 which encircles the bore 19 and an outer refractory jacket 27 which surrounds the lower end of the steel shell 25.,

The jacket 27 is provided to prevent the steel shell 25 from being damaged by direct contact with the molten metal 12 and for this reason jacket 27 extends below the lower end of shell and merges with the lining 26. The refractory lining 26 and the outer refractory jacket 27 are formed by forcing a high alumina refractory ram` mix between a mold and the steel shell 25.

An induction coil 28 is embedded within the refractory lining 26 of the nozzle 18 and consists of a number of-turns of relatively heavy copper wire 29 which may be hollow to per-mit the circulation of a suitable cooling fluid. The coil 28 is spaced from the steel 25 and is electrically insulated therefrom by the refractory lining 26.

The coil 28 is connected to a suitable source of alternating current (not shown). This will produce a magnetic field B extending through the bore 19 :of the pipe 18. As `those skilled in `the art will appreciate, the margnetic field B will change with time as the current in the coil 28ialternates.

Assume, for the sake of illustration, that` the magnetic flux B is increasing in the directions shown by the arrows in FIG. 2. This will induce eddy currents, i.e., within the moltenmetal 12 disposed in the bore 18 as illustrated in FIG. 2. These eddy currents flowing through the molten metal within the bore 19 of the molten metal conducting pipe 18 will tend to heat this portion of the melt.

Because the `winding 28 is embedded within the lining 26 `of the nozzle 18, it in no way impedes relative move- -ment between the vessel 10 and the ladle 11. Also, the refractory lining 26 shields the coil 28 from the molten metal 12.

A second induction coil 30 may also be provided in the jacket 27 for heating the metal in the ladle 11. The winding 30 will also be connected to a suitable alternating current source (not shown) so that a magnetic field Bewill be produced in the molten metal 12 surrounding the lower end of the pipe 18. If the `magnetic flux B is increasing in the direction shownby the arrows in FIG. 2, an eddy current, i.e., will be induced `which heats the molten metal 12. The coil 30 is also spaced from the steel shell 25 and is electrically insulated therefrom by the refractory jacket 27.

In prior art arrangements, induction heaters employed with vacuum degassing vessels of the generaltype Wherein molten metal is drawn into and dischargedfrom a vacuum vessel by means `of molten metal conducting pipes, a plurality of such pipes were required. Thus, while the instant invention is usable with a vacuum degassing vessel having any number of molten metal conducting 4 pipes, it may be employed with a device having a single pipe. Also, the heating assembly according to the instant invention is not limited to the illustrated method of conveying molten metal into the degassing chamber 10 but is also usable with apparatus employing other methods such as the use of aninert gas.

While only a single embodiment of the invention has been illustratedand described, it is not intended to be limited thereby but only by the scope of the appended claims.

I claim:

1. In a refractory lined vacuum degassing vessel having a pipe extending downwardly therefrom and opening into the interior thereof for conducting molten metal to and from the interior thereof from a container of saidv metal disposed therebelow, said pipe having a metallic shell and a refractory lining having a central bore, a refractory jacket surrounding the lower end of said metallic shell, said refractory lining and said refractory jacket forming a continuous ceramic covering about the lower end portion of said metallic shell, and first and second induction coils embedded in, respectively, said lining and jacket and below the surfaces thereof in surrounding relation to said bore and said shell, and said coils being spaced from said metallic shell.

2. In a refractory lined vacuum degassing vessel according to claim 1, wherein said rst and second coils are energized to create ux fields in the bore and outwardly adjacent the jacket, respectively, that are disposed in opposite directions to one another.

3. Apparatus for degassing molten metal comprising a refractory lined vessel defining a chamber, 'means for evacuating said chamber to produce a partial vacuum therein, a container for said molten metal disposed below said chamber, a molten metal conducting pipe alixed to the bottom of said vessel and opening into the lower end of said chamber, said container and said chamber being relatively movable toward and away from each other so that the lower end of said pipe may be immersed into said molten metal, a refractory lining disposed on the inner surface of said pipe and having a longitudinal bore formed therein, a first induction coil embedded within said lining and encircling the bore formed therein, said coil being spaced from said pipe, a refractory jacket surrounding the lower end of said` pipe, said refractory lining and said refractory jacket forming a continuous refractory covering over the lower end portion of said pipe which is subject to immersion in molten metal, and a second induction coil embeded within said jacket and surrounding the lower end of said pipe, said second induction coil being spaced from said pipe.

4. Apparatus for degassing molten metal according to claim 3, wherein said first and second coils are energized to create flux fields in the bore and outwardly adjacent the jacket, respectively, that are disposed in opposite directions to one another.

References Cited UNITED STATES PATENTS 2,837,790 6/1958 Rozian 266-34 X 3,062,523 11/1962 Knuppel 75--49 X 3,146,288 8/1964 Gero 266-34 3,246,889` 4/ 1966 Sieckman et al. 266--34 FOREIGN PATENTS 801,519 9/1958 Great Britain.

WILLIAM I. STEPHENSON, Primary Examiner.

E. MAR, Assistant Examiner. 

1. IN A REFRACTORY LINED VACUUM DEGASSING VESSEL HAVING A PIPE EXTENDING DOWNWARDLY THEREFROM AND OPENING INTO THE INTERIOR THEREOF FOR CONDUCTING MOLTEN METAL TO AND FROM THE INTERIOR THEREOF FROM A CONTAINER OF SAID METAL DISPOSED THEREBELOW, SAID PIPE HAVING A METALLIC SHELL AND A REFRACTORY LINING HAVING A CENTRAL BORE, A REFRACTORY JACKET SURROUNDING THE LOWER END OF SAID METALLIC SHELL, SAID REFRACTORY LINING AND SAID REFRACTORY JACKET FORMING A CONTINUOUS CERAMIC COVERING ABOUT THE LOWER END PORTION OF SAID METALLIC SHELL, AND FIRST AND SECOND INDUCTION COILS EMBEDDED IN, RESPECTIVELY, IN LINING AND JACKET AND BELOW THE SURFACES THEREOF IN SURROUNDING RELATION TO SAID BORE AND SAID SHELL, AND SAID COILS BEING SPACED FROM SAID METALLIC SHELL. 